How to Determine Size of Greenhouse Plastic You Need | Two Methods

Figuring out what size greenhouse plastic you need to successfully cover your high tunnel, hoop house, or greenhouse is fairly simple. It is a matter of determining the width and length of material... plus any required excess to ensure you have enough.

To help you figure out what size cover you need, this post provides two different methods:

  • Method one: Will help you figure out how to get all the required plastic in ONE piece
  • Method two: Will help you figure out how to determine pieces for your end walls and top cover SEPARATELY

Regardless of the method you choose, one thing is certain: You don't want to be short greenhouse filmLet's jump into the different methods for calculating greenhouse plastic sizes.

METHOD ONE: One Piece of Greenhouse Plastic for Your End-Walls and Top-Cover

Greenhouses, hoop houses, and high tunnels typically need their end-walls AND top section covered in greenhouse film.  It is relatively easy to calculate how much plastic is required to completely cover your structure and provide a extra to account for possible mis-steps. 

Step One: Figure Out Greenhouse Plastic Width

Step Two: Figure Out Greenhouse Plastic Length

Here is an example of what the length requirements would be for the above picture:

  • A = 72 ft. 
  • B = 9 ft.

So... 72 ft. + 9 ft. + 9 ft. + 8 ft. = 99 ft. 

You will require a minimum length of 99 ft. Remember that the 8 ft. provides required excess material for each end... you don't want to be too short.

Step Three: Use Measurements to Pick a Greenhouse Film Cover

Now you know your required cover width using  "X" + 4 ft.

Now you know your required cover length using "A" + "B" + "B" + 8 

Based on the examples we used above, we need a plastic cover size that is a minimum of 24 ft. wide x 99 ft. long. Since most greenhouse plastic lengths are available in 5 ft. increments we can round the length up to 100 ft. long. The plastic we need to order for the example outlined in the steps above is a 24 ft. wide x 100 ft. long.

Here are some options for greenhouse film we could use

If you aren't sure which plastic cover is right for your high tunnel, you can check out our post on the best greenhouse plastic for high tunnels and hoop houses. We put that post together after years of making DIY Kits and building them across the country. 

METHOD TWO: Calculate for Separate End-Wall and Top Cover Pieces

If you decide to use this method, you will end up SAVING greenhouse plastic. The reason? Your end-wall width is always going to be slightly less than the measurement over-the-top of your structure. 

For this reason, the method below is great for someone looking to reduce the amount of plastic waste they use on their project.

Step One: Determine End-Wall Sizes

Step Two: Determine Top Cover Size

Step Three: Use Measurements to Pick Greenhouse Cover

Using the above method for selecting your greenhouse covers will result in the need for two OR three pieces of greenhouse plastic. 

Two pieces would be required if... you plan to get one piece that includes enough length for you to cut both your end-walls out of AND you would need a separate piece for your top cover. 

For example: One piece that is 22 ft. wide x 22 ft. long would be wide enough and long enough to derive BOTH 22 ft. x 11 ft. end-wall pieces out of. A second piece that is 32 ft. wide x 74 ft. long could be used for your top cover

Three pieces would be required if... you plan to get one piece for each end-wall AND you would need the third piece for your top cover. 

For example: If you want both of your end-wall plastic covers to be cut separately and in advance, you would need two 22 ft. wide x 11 ft. long plastic pieces; one for each end. A third piece of plastic, size 32 ft. wide x 74 ft. long would be required for your top cover. 

Most Greenhouse Plastic Comes in Standard Widths

For the most popular greenhouse plastic covers, there are standard widths you can select from. If your exact width requirement isn't listed, you can simply round-up to the next available width. You can browse standard 4 year 6 mil Clear Greenhouse Plastic width options or 4 year 6 mil IRAD Greenhouse Plastic standard width options. 

If you are interested in a more precisely cut greenhouse plastic covering for your tops or ends, the 9 mil AC Clear Woven Greenhouse Plastics and 12 mil AC Clear Woven Greenhouse Plastics are available in ANY width and ANY length. 

In other words... the 9 mil and 12 mil options can be custom cut. If you want a quote on a specific size not listed on the product pages you can email us what you are looking for at or call us at (833) 886-6351 ext. 2.